Method and an arrangement for recognizing an object or its position and orientation in space

ABSTRACT

A method and apparatus for determining the positional changes in the surface of an object by recording a real image and speckle pattern produced by focusing the radiation scattered by the object from a coherent source, and by comparing the object with the recorded image and the resulting speckle pattern.

United States Patent Groh [ 1 May9, 1972 [54] METHOD AND AN ARRANGEMENTFOR RECOGNIZING AN OBJECT OR ITS POSITION AND ORIENTATION IN SPACE [72]Inventor: Gunther Groh, Hamburg, Germany [73] Assignee: U.S. PhilipsCorporation, New York, NY.

[22] Filed: Feb. 6, 1969 [21] Appl.No.: 797,103

[30] Foreign Application Priority Data Feb. 9, 1968 Germany ..P 16 73927.8

[52] US. Cl.. ..356/162, 356/152, 356/172 [51] Int. Cl. ..G01b 11/00[58] Field ofSearch ..356/4, 5, 152,162, 172, 29,

[56] References Cited UNITED STATES PATENTS 3,388,259 6/1968 Flower..356/2l2 3,490,827 1/1970 Van Ligten et al. ..350/3.5

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Cutler, C. C., International Science & Tech. 9/63 pp. 54- 63.

Martienssen et al., Physics Letters, Vol. 24 A, No. 2, 1/67, pp. 126 8.

Gerritsen et al., Applied Optics, Vol. 7, No. 11, 11/68, pp. 230- 231 l.

Rosen et a1., Applied Physics Letters, Vol. 10, No. 5, 3/67, pp. 140-142.

Collier et al., Applied Physics Letters, Vol. 8, No. 2, 1/66, pp. 44-46.

Ennos, A. E., Contemp. Phys, Vol. 8, No. 2, 3/67, pp. 153- 170.

Brooks, R. E., Electronics, 5/67 pp. 88- 93.

Gottenberg, W. C., Experimental Mechanics, Vol. 8, 9/68, pp. 405-410.

R. E. Brooks, New Dimensions for Interferometry, Electronics, May 1967.

W. G. Gottenberg, Some Applications of Holographic Interferometry,Experimental Mechanics, Vol. 8, Sept. 1968.

Primary Examiner-Ronald L. Wibert Assistant Examiner-Jeff RothenbergAnomey-Frank R. Trifari ABSTRACT A method and apparatus for determiningthe positional changes in the surface of an object by recording a realimage and speckle pattern produced by focusing the radiation scatteredby the object from a coherent source, and by comparing the object withthe recorded image and the resulting speckle pattern.

9 Claims, 2 Drawing Figures PATENTEDMY 9 I972 INVENTOR.

GUNTHER GROH METHOD AND AN ARRANGEMENT FOR RECOGNIZING AN OBJECT OR ITSPOSITION AND ORIENTATION IN SPACE The invention relates to a method ofrecognizing an object or its position and orientation in space and toarrangements for carrying out the method. Such methods are required, forexample, when in manufacture an object after being machined has to bereturned to its previous position. In addition, such methods arerequired in many measuring problems in which for example a change inlength, an angular variation or the like is to be measured. Further, themethod to be described may be used in analyzing vibrations of bodies andchanges of materials.

Several methods of recognizing the position and the orientation of anobject in space are known. In the optical methods generally markssuitably made on the object are made to coincide with marks previouslymade (for example cross hairs) by means of image formation. The positionand orientation then are related to these previous marks.

These methods have several disadvantages.

Firstly, they require subjective observation, i.e. an observer has todecide which changes in position and orientation lead to a better andultimately to the best coincidence of the images and the original marks.Hence, the adjustment cannot readily be automatized. In addition, withrespect to the adjusting speed and in estimating rapid changes inposition and orientation limits are set by the speed of response of thehuman eye.

Secondly, in positioning with the use of more than one degree offreedom, for example, linear and rotary movements, a correspondingnumber of reference marks with associated image forming systems arerequired. The marks made on the object must be made to coincide with thereference marks in several adjusting cycles. A simple indication of theposition of the body is not possible.

Thirdly, suitable marks must be made on the object unless this happensto contain sufiiciently characteristic structures to be used as targetsfor adjusting.

These disadvantages of known methods are avoided by the use of theinvention. In addition, the method proposed permits further unknownuses.

The method in accordance with the invention is characterized in that theintensity distribution produced by coherent waves being scattered fromthe object is recorded and stored and in that the intensity distributionas changed by a change in the object or in its position and orientationis compared with the stored distribution.

Since the stored intensity distribution contains the information aboutthe scattering properties of the illuminated parts of the object andabout their positions and orientations relative to the incident waves,both the object and its place and orientation are unambiguouslydetermined. In order to recognize an object or its positionalcoordinates the intensity distribution produced by scattering from theobject to be investigated is compared with the stored distribution. Thereference system in which the measuring values are determined is definedby the incident waves and by the position and form of the recordingdevice. Hence, the properties of the wave and of the recording deviceand their relative positions must be maintained constant within thedesired measuring accuracy. On the other hand, the reference system as awhole may be arbitrarily moved in space. The position and orientation ofthe store also is insignificant provided that the store is not identicalwith, or rigidly connected to, the recording apparatus.

The method may be carried out with any kind of coherent waves (forexample, acoustic or electromagnetic waves or corpuscular radiation ofwidely different wavelengths). In each individual case, there may beoptimum adaptation of the method to the respective problem by the choiceof the physical nature and the wavelength of the waves used. Therefore,in the following embodiments given by way of example laser radiation isused only for the sake of clarity and the invention is not to beunderstood to be restricted thereto.

For the uses of the method, two quantities are important: the measuringsensitivity and the measuring range. The latter is determined by thatmagnitude of the change in the scattering properties or in the positionand orientation of the object at which there is, if only just, ameasurable correlation between the intensity distribution as stored andas measured, permitting, for example, the object to be moved in thedirection of increasing correlation so as to obtain correct positioningof the object. The measuring sensitivity is determined by the magnitudeof the change by which the comparing signal responds to incorrectpositioning of the object. According to the invention, both magnitudesmay be predetermined within wide limits by the choice of the number andof the properties of the irradiating waves (for example their physicalnature, wavelength, state of polarization, angle of convergence ordivergence, beam diameter). Furthermore, the measuring sensitivity andthe measuring range may be influenced in a desirable manner by theformation of certain scattering properties (for example preferreddirections, periodic fractions) of the irradiated parts of the object.

A few particular arrangements for carrying out this method will now bedescribed.

In a given arrangement (see FIG. 1, in which only a single beam isshown) one or more laser beams 1 are directed on to the object 2. Theangle of convergence 3 and the transverse dimension of the irradiatedarea may be adjusted by means of an optical system 4, as may be thestate of polarization. The intensity distribution of the scattered light5 due to the characteristic granulation is recorded in a photographicemulsion 6 and after development is stored therein. Since by thephotographic process a negative of the intensity distribution isobtained, ideally (i.e. in a linear photographic process) the light 5scattered from the object 2 is completely intercepted, i.e. theintensity of the transmitted light 8 made to converge, for example, by alens 7 is a minimum and in the ideal case is zero. A change in thescattering properties of the object or in its position and orientationresults in an increase in intensity, which can be measured by means of aphotosensitive detector 9 and an indicating device 10. The usual form ofthe output signal y (intensity) of this cross-correlator measured as afunction of a variation x (for example the distance travelled) is shownin FIG. 2. The measuring range 11 is determined by the width ofthis'cross-correlation function and depends not only on the propertiesof the light and the scattering properties of the object but also on thenature of the change. For example, on irradiation with a collimatedlaser beam a variation in depth is detected with a sensitivity smallerby several orders of magnitude than is a lateral displacement of theobject. In many applications such properties may be utilized. On theother hand, in the embodiment described the sensitivity may be increasedby using more than one laser beam or by employing larger angles ofconvergence.

So far only the natural scattering properties of the object have beenused. However, frequently certain portions of the object may be givenparticularly advantageous scattering properties. It may, for example,readily be ensured that the roughness of the scattering surface has twopreferred directions. In this case, the intensity distribution of thescattered light contains, in addition to the usual granulation, a crosspattern of higher luminous intensity, which enables, for example, arotation of the object to become directly visible. In order to increasethe measuring range with constant measuring sensitivity, it may be ofadvantage to superimpose a periodic fraction on the statistic roughness,for example by ruling a grating on the rough surface. Thecross-correlation function of the granulation then also includes aperiodic fraction so that the measuring range is increased.

In another arrangement according to the invention the photographic plate6 shown in FIG. 1 is replaced by the photocathode of a television cameratube, the intensity distribution being stored in a television imagestore. The changed intensity distribution is compared in an electric oroptic correlator. By electric means the difference is more readilyformed, an image of the difference being displayed on a monitor forcomparison. in addition, the value of the positive portions of theintensity of the difference image averaged over an image may beindicated as a measure of the deviation from the original scatteringproperty or from the position and orientatron.

By a person acquainted with the invention the arrangements described mayreadily be modified so as to deal with the problem to be solved in therespective case.

The invention further permits of carrying out several novel methodswhich will be described hereinafter.

By way of example, the change in position and orientation of the objector of a part of the object may be measured without physical contact, thetransmitter and receiver being measurably displaced in a manner suchthat optimum correspondence between the intensity distribution as storedand as measured will be produced. For this purpose, any unmachinedsurface of the body may be used. No additional marks are required, sincethe granulation (similarly to a finger print) inherently contains theinformation about the surface element.

Furthermore the method may be used for contactless measurement ofvibrations of the object by recording and storing the granulation of theobject when stationary and by analyzing variations of thecross-correlation function with time of the object when vibrating.

In a further group of uses the position and orientation of the bodyremain constant. In these cases, a change in the crosscorrelationfunction or a similar comparison function is produced by a change in thescattering properties of the body. For example, a given object may berecognized amongst similar objects without special marks having to bemade on it. In another use, fatique phenomena in stressed materials maybe investigated by using the change in the scattering properties of thematerial as a measure of the fatique. The variation of corrosion orsedimentation phenemena with time may also be tracked at a time at whichthe image observed under a microscope shows no or very little change,for since the granulation is caused by the interference of the scatteredradiation, even slight variations of the optical path length aresufiicient to influence the granulation.

ln uses based on measurements of the changes in the scatteringproperties it is of advantage for one or more positional coordinates tobe periodically changed by an amplitude exceeding the measuring range 11which occurs in the respective case or for the laser beam to becorrespondingly moved. Thus, a periodic signal at twice the frequencyhaving an amplitude proportional to the maximum correlation is producedat the output ofthe cross-correlator.

What is claimed is:

1. A method of determining positional changes in the surface of anobject, comprising exposing the object surface to coherent radiation toproduce a speckle pattern, exposing a light image recording filmdirectly and only to radiation scattered from said object surface torecord said speckle pattern thereon, exposing the object a second timeto the coherent radiation to produce a second speckle pattern, andcomparing the intensity distribution of the recorded speckle patternwith that of the second speckle pattern from the object.

2. A method as claimed in claim 1, wherein the step of comparing therecorded speckle pattern with the second speckle pattern from the objectcomprises subtracting the recorded light intensity of the image fromcorresponding portions of the second speckle pattern from the object,and displaying the resultant intensity distribution.

3. A method as claimed in claim 1, wherein the step of comparing therecorded speckle pattern with the second speckle pattern from the objectcomprises vibrating the object with an amplitude exceeding thepositional measuring range.

4. A method as claimed in claim I, wherein the step of comparing therecorded speckle pattern with the second speckle pattern from the objectcomprises moving the recorded pattern to a osition where the amplitudeof the cross-correlation function etween the recorded speckle patternand the second speckle pattern from the object is at a maximum.

5. A method as claimed in claim 1, wherein the step of recording theresultant speckle pattern comprises exposing a photographic emulsion tothe speckle pattern, and wherein the step of comparing the recordedspeckle pattern with the second speckle pattern from the objectcomprises imaging the object on the developed negative resulting fromthe exposure.

6. A device for determining the positional changes in the surface of anobject, comprising a source of coherent radiation, means for directingthe radiation from the source to the object whereby the radiation isscattered from the object to produce a speckle pattern, a light imagerecording film located in a plane in space for directly receiving onlythe radiation scattered from the object, whereby the speckle pattern ofthe object is recorded on said film, and means for comparing theintensity distribution of the recorded speckle pattern with theintensity distribution of radiation scattered from the object at a latertime.

7. A device as claimed in claim 6, wherein the recording film is aphotographic emulsion.

8. Apparatus as claimed in claim 7, wherein the means for comparing therecorded speckle pattern with the radiation scattered from the objectcomprises a photo-sensitive measuring device located on the side of thephotographic emulsion opposite the object.

9. A device as claimed in claim 6, further comprising a periodicfunction on the surface of the object to be measured.

UNITED STATES PATENT OFFICE CERTIFICATE OF ceEcTmN Patent No. 3 66] 465Dated May 9, 1.972

Inventor-(s) GUNTHER GROH It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Claim 2, line 4, cancel "image" and insert recorded speckle pattern--.

Signed and eal d thi 25th day of July 1972.

(SEAL) Attest.

EDWARD M.FLETCHER,JR ROBERT GOTTSCHALK Commissioner of Patents AttestingOfficer mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 35 1.4 5 Dated May 9, 1972 Inventor( GUNTHER GROH It is certifiedthat error appears in the aboveidentified patent and that said LettersPatent are hereby corrected as shown below:

Claim 2, line 4, cancel "image" and insert --recorded speckle pattern-.

Signed and sealed this 25th day of July 1972.

(SEAL) Attest:

EDWARD M.FLEI'CHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. A method of determining positional changes in the surface of anobject, comprising exposing the object surface to coherent radiation toproduce a speckle pattern, exposing a light image recording filmdirectly and only to radiation scattered from said object surface torecord said speckle pattern thereon, exposing the object a second timeto the coherent radiation to produce a second speckle pattern, andcomparing the intensity distribution of the recorded speckle patternwith that of the second speckle pattern from the object.
 2. A method asclaimed in claim 1, wherein the step of comparing the recorded specklepattern with the second speckle pattern from the object comprisessubtracting the recorded light intensity of the image from correspondingportions of the second speckle pattern from the object, and displayingthe resultant intensity distribution.
 3. A method as claimed in claim 1,wherein the step of comparing the recorded speckle pattern with thesecond speckle pattern from the object comprises vibrating the objectwith an amplitude exceeding the positional measuring range.
 4. A methodas claimed in claim 1, wherein the step of comparing the recordedspeckle pattern with the second speckle pattern from the objectcomprises moving the recorded pattern to a position where the amplitudeof the cross-correlation function between the recorded speckle patternand the second speckle pattern from the object is at a maximum.
 5. Amethod as claimed in claim 1, wherein the step of recording theresultant speckle pattern comprises exposing a photographic emulsion tothe speckle pattern, and wherein the step of comparing the recordedspeckle pattern with the second speckle pattern from the objectcomprises imaging the object on the developed negative resulting fromthe exposure.
 6. A device for determining the positional changes in thesurface of an object, comprising a source of coherent radiation, meansfor directing the radiation from the source to the object whereby theradiation is scattered from the object to produce a speckle pattern, alight image recording film located in a plane in space for directlyreceiving only the radiation scattered from the object, whereby thespeckle pattern of the object is recorded on said film, and means forcomparing the intensity distribution of the recorded speckle patternwith the intensity distribution of radiation scattered from the objectat a later time.
 7. A device as claimed in claim 6, wherein therecording film is a photographic emulsion.
 8. Apparatus as claimed inclaim 7, wherein the means for comparing the recorded speckle patternwith the radiation scattered from the object comprises a photo-sensitivemeasuring device located on the side of the photographic emulsionopposite the object.
 9. A device as claimed in claim 6, furthercomprising a periodic function on the surface of the object to bemeasured.